1. Field of the Invention
This invention resides in the field of rocket motors that contain two or more grains, with adjacent grains separated by a removable barrier.
2. Description of the Prior Art
Rocket motors with two or more propellant grains that are ignited individually are useful when a second or subsequent propulsive impulse is needed at an interval of time after the first propulsive impulse. Anti-aircraft missiles utilize the second impulse to provide extra velocity and to increase the maneuverability of a missile just before the missile intercepts a target. Missiles that are designed for both long and short range also benefit from successive pulse capability since the second pulse can either be fired simultaneously with the first for short-range missions or delayed for firing later in the missile trajectory for long-range missions, minimizing the peak velocity and thereby the drag on the missile. Rockets offering two or more pulses are also useful for missiles whose maximum velocity is limited due to structural or thermal considerations, the individual pulses dividing the thrust by time intervals to prevent the velocity from exceeding the maximum.
The capability of successive pulses can be built into a rocket motor in a variety of ways. One way is to equip the rocket motor with separate combustion chambers, each chamber having a separate nozzle. Another is to divide the rocket motor chamber into separate subchambers separated by an interstage bulkhead with one or more orifices blocked by a plug that is ejected when the igniter in the second or subsequent subchamber is fired. A third way is to equip the rocket motor with two radial-burning propellant charges separated by an insulating barrier that is opened when the second propellant charge is fired. The most common way of achieving successive pulses however is by the use of a multi-stage rocket motor in which separate rocket components are individually ignited and then jettisoned after use. A disadvantage of a multi-stage rocket motor is that the aft end components of the guidance system, such as nozzles and fins, are also jettisoned. Successive pulses can also be achieved in a single-chamber rocket motor by the inclusion of an insulated end-burning or center-perforated second stage that is separated from the initial burning stage by a frangible barrier that is ruptured when the second stage is ignited. The present invention is an improvement on such a single-stage rocket motor.
Of further relevance to this invention are rocket motors and other flight vehicles with thrust vectoring capability. Flight vehicles are often fired at targets that are maneuverable and thereby capable of evading the vehicles. Many targets are also capable of firing back at a flight vehicle as the flight vehicle approaches. Thrust vectoring, or attitude maneuverability, provides the flight vehicle with the ability to respond to both such target maneuvers, i.e., to maintain its aim toward the target, to avoid being fired upon, or both. One method of achieving attitude maneuverability is by the use of side-facing thrusters, also known as “divert motors,” that are controllable independently of the forward-thrusting propellant.